SYNOPSIS :
    tunnel.bash
        --help
        --configure
        --local-port    <LOCAL_PORT>
        --remote-port   <REMOTE_PORT>
        --local-to-remote
        --remote-to-local
        --remote-user   <REMOTE_USER>
        --remote-host   <REMOTE_HOST>
        --identity-file <IDENTITY_FILE>

DESCRIPTION :
    --help               Help page
    --configure          Config remote server to support forwarding (optional)
                         This option will require arguments '--remote-user' and '--remote-host'
    --local-port         Local port number (require)
    --remote-port        Remote port number (require)
    --local-to-remote    Forward request from local machine to remote machine
                         Either '--local-to-remote' or '--remote-to-local' must be specified
    --remote-to-local    Forward request from remote machine to local machine (require)
                         Either '--local-to-remote' or '--remote-to-local' must be specified
    --remote-user        Remote user (require)
    --remote-host        Remote host (require)
    --identity-file      Path to private key (*.ppk, *.pem) to access remote server (optional)

EXAMPLES :
    ./tunnel.bash --help
    ./tunnel.bash
        --configure
        --remote-user 'root'
        --remote-host 'my-server.com'
    ./tunnel.bash
        --configure
        --remote-user 'root'
        --remote-host 'my-server.com'
        --identity-file '/keys/my-server/key.ppk'
    ./tunnel.bash
        --local-port 8080
        --remote-port 9090
        --local-to-remote
        --remote-user 'root'
        --remote-host 'my-server.com'
    ./tunnel.bash
        --local-port 8080
        --remote-port 9090
        --remote-to-local
        --remote-user 'root'
        --remote-host 'my-server.com'
    ./tunnel.bash
        --local-port 8080
        --remote-port 9090
        --remote-to-local
        --remote-user 'root'
        --remote-host 'my-server.com'
        --identity-file '/keys/my-server/key.ppk'